Download Presentation

Skeletal Muscle - 1

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

Animation of this process at: http://www.sci.sdsu.edu/movies/actin_myosin.html

Actin myosin contraction

http://www.sci.sdsu.edu/movies/actin_myosin.html

Actin myosin contraction

http://www.octc.kctcs.edu/gcaplan/anat/images/Image336.gif

Sarcoplasmic reticulum

YC Fung, Biomech, 1993

Cross-bridge cycle

To form a cross-bridge:

Ca2+ is released from long tubules of sarcoplasmic reticulum

Ca2+ binds to troponin

Allows topomyosin thread to reconfigure

Exposes binding site

# of sites determined by concentration of Ca2+

Cross-bridges bend to pull actin filament inward

When maximum range of bending reached, bridge connection is broken

Globular head returns to oblique angle

Connection to new binding site can be established

Numerous cycles are required for complete shortening

Cells and formation of myofibers

J Huard et al., JBJS, 2002

Histology

Innervation

https://courses.stu.qmul.ac.uk/smd/kb/

J Huard et al., JBJS, 2002

Innervation

Motor unit (MU) consists of all fibers innervated by one single motor nerve fiber

Small precise muscles 2-3 muscle fibers/MU

Large muscles, up to 1000 muscle fibers/MU

Feedback via muscle spindles to sense tension in the sensory peripheral nervous system

Contractions

J Huard et al., JBJS, 2002

Contraction cycle

Action potential (AP) at neuromuscular junction Muscles can not push, they may only only CONTRACT (pull)A muscle contraction is called a muscle TWITCH

http://fig.cox.miami.edu/~cmallery/150/neuro/sf43x16.jpg

Muscle contraction

To increase strength of contraction

Recruit more motor units

Increase stimulation frequency (wave summation)

Efficiency of muscle contraction

20-25% of metabolic energy becomes mechanical work

75-80% becomes heat

Isotonic contractions – same force

Isometric contractions – “same” length

Eccentric contractions – lengthening

Concentric contractions – shortening

Length-tension relationship (sarcomeres)

Optimum overlap

Few available binding sites

No available binding sites

Fewer binding sites due to overlap

Not continuous F-L curve

Isometric forces at max stimulation

at various lengths

W Herzog, Muscle Mechanics

Anatomy of leg muscles

Grey’s Anatomy

http://en.wikipedia.org/wiki/Image:Illu_lower_extremity_muscles.jpg

Muscle types

Two main types of fibers

Differ in the mechanism they use to produce ATP

Amount of each type varies from muscle to muscle and from person to person

Red ("slow-twitch") fibers have more mitochondria, store oxygen in myoglobin, rely on aerobic metabolism, have a greater capillary to volume ratio and are associated with endurance; these produce ATP more slowly. Marathon runners tend to have more red fibers, generally through a combination of genetics and training.

White ("fast-twitch") fibers have fewer mitochondria, are capable of more powerful (but shorter) contractions, metabolize ATP more quickly, have a lower capillary to volume ratio, and are more likely to accumulate lactic acid. Weightlifters and sprinters tend to have more white fibers.

ATP Production Strategies

Aerobic – ATP produced by breakdown of precursors in the presence of O2